Recycling Method of Sludge Recovery Oil

ABSTRACT

Provided is a recycling method of recovery oil including: a) recovering sludge accumulated in a crude oil tank; b) separating the sludge into recovery oil, water, and sediment; and c) mixing the recovery oil with crude oil and performing fractional distillation on a mixture of the recovery oil and the crude oil.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No. 10-2014-0069092 filed Jun. 09, 2014, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The following disclosure relates to a recycling method of recovery oil. More particularly, the following disclosure relates to a recycling method of recovery oil capable of recycling the recovery oil and expecting a profitability improving effect by recovering the recovery oil from sludge accumulated in a crude oil tank and then mixing the recovery oil with crude oil.

BACKGROUND

Generally, crude oil, which means petroleum in a natural state coming out of an oil well without being subjected to a processing process or a refining process, indicates a sticky liquid having several hydrocarbon compounds as a main component and having a blackish brown color. The crude oil includes impurities such as sulfur, oxygen, a nitrogen compound, a metal, moisture, gas, and the like, as well as the hydrocarbon compounds, which are the main component. These impurities are mixed with rust generated from a pipe or a tank wall at the time of transferring the crude oil, a naturally generated solid material, an insoluble material, and the like, such that they become sludge and are accumulated on a lower portion of a storage tank.

A crude oil storage tank of an oil refinery should compulsorily undergo a periodic test at a period of generally 8 to 10 years due to a risk of oil spill by a leak, even though the period is different for each nation. In this case, crude oil sludge accumulated in the crude oil storage tank is cleaned and discharged. In addition, in the case in which an oil spill accident is generated in spite of this previous periodical test, the sludgy should be cleaned in order to repair the crude oil storage tank. Since the sludge is generally generated and accumulated at a rapid speed, it is accumulated in the crude oil storage tank and decreases a utilization space in the crude oil storage tank. In addition, when the sludge is not removed for a long period of time, such that it is accumulated at height of a crude oil outlet, the sludge overflows the tank to be introduced into the subsequent process, thereby having a negative influence on an entire process. Particularly, when a level of the sludge becomes higher than the height of the crude oil outlet, a large amount of sludge is introduced into a process in an instant, which causes a problem such as a crude oil charge pump trip, and the like. In addition, when the sludge is introduced into the process, many negative influences such as a decrease in a lifespan of a heat exchanger in the process, a decrease in a lifespan of a catalyst, throughput loss due frequent filter driving of a catalyst process, and the like are caused.

It is important to process and discard the sludge as well as remove the sludge from the tank. As a method of processing the sludge, there are an incineration method, a physical refining method using a refinery, or the like, chemical refining method of processing the sludge using iso oxane and gas oil, and the like. However, recovery oil separated by the above-mentioned refining methods has a limitation in being used due to a high pour point and a high content of impurities. In addition, there are several limitations in operating a processing process such as securing a margin tank, or the like.

RELATED ART DOCUMENT Patent Document

U.S. Pat. No. 04,014,780 (Mar. 29, 1977)

U.S. Pat. No. 05,085,710 (Feb. 4, 1992)

SUMMARY

An embodiment of the present invention is directed to providing a recycling method of recovery oil capable of overcoming disadvantages of the recovery oil such as a high pour point, a low flash point, and a high content of impurities and expecting a profitability improving effect by recovering the recovery oil from sludge accumulated in a crude oil tank and then mixing the recovery oil with crude oil.

In one general aspect, a recycling method of recovery oil includes: a) a step of recovering sludge accumulated in a crude oil tank; b) a step of separating the sludge into recovery oil, water, and sediment; and c) a step of mixing the recovery oil with crude oil and performing fractional distillation on a mixture of the recovery oil and the crude oil.

In the step c), the recovery oil and the crude oil may be mixed with each other by any one or two or more selected among c1) a method of mixing the recovery oil with the crude oil using a line mixer and transferring the mixture to a charge pump; c2) a method of periodically mixing the recovery oil with the crude oil and transferring the mixture to the charge pump; and c3) a method of mixing the recovery oil with the crude oil passing through the charge pump and transferring the mixture to a desalter.

Exemplary embodiments described above are not limited to contents described above, but include all contents that may be easily changed by those skilled in the art. As an example, there may be a case of using another type of apparatus in order to execute the same technology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 illustrate a process of mixing recovery oil and crude oil with each other according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a recycling method of recovery oil according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. The accompanying drawings to be provided below are provided by way of example so that the idea of the present invention can be sufficiently transferred to those skilled in the art to which the present invention pertains. Therefore, the present invention is not limited to the accompanying drawings provided below, but may be modified in many different forms. In addition, the accompanying drawings suggested below will be exaggerated in order to clear the spirit and scope of the present invention. In addition, like reference numerals denote like elements throughout the specification.

Technical terms and scientific terms used in the present specification have the general meaning understood by those skilled in the art to which the present invention pertains unless otherwise defined, and a description for the known function and configuration unnecessarily obscuring the gist of the present invention will be omitted in the following description and the accompanying drawings.

First, a recycling method of recovery oil according to an exemplary embodiment of the present invention may include a) a step of recovering sludge accumulated in a crude oil tank; b) a step of separating the sludge into recovery oil, water, and sediment; and c) a step of mixing the recovery oil with crude oil and performing fractional distillation on a mixture of the recovery oil and the crude oil.

The crude oil used in the present invention generally means a combustible liquid existing in a natural state in the ground and having a brown to black color. In addition, the crude oil may include several types of hydrocarbons and impurities, and components of the crude oil may be changed depending on a drilling region and a kind of hydrocarbon. However, the present invention is not limited thereto.

Properties of the sludge accumulated in the crude oil tank may be changed depending on stored crude oil, a cleaning period, and the like. In addition, a method of recovering the accumulated sludge may also be changed. For example, in the case of light oil, a small amount of sludge is generated, and the sludge may be cleaned using water. In the case of medium oil, the sludge and oiliness on a wall surface may be dissolved and removed using light oil. Further, in the case of bunker oil, since the sludge is in a solid-phase at room temperature, the sludge solidified on the bottom of the crude oil tank may be dissolved and removed.

The sludge according to the present invention may contain 5 to 28 wt % of water, but is not limited thereto. In the case of pure sludge, that is, sediment, a content of asphaltene or inorganics may be 2 to 38 wt %. Particularly, these inorganics include iron (Fe) as a main component, and an iron component in these inorganics may be increased due to corrosion of the crude oil tank as a tank storage time becomes long. In addition to these components, a wax component, sand, other coke precursors, and the like, may be further included in the sludge.

The asphaltene, which is a component insoluble in n-hexane and soluble in toluene, may be sunk as a solid particle in the crude oil to form the sludge or form emulsion together with a heavy ingredient such as a resin, or the like, and moisture. Particularly, in the case in which the asphaltene is sunk as the solid particle, the asphaltene present in an emulsion form is mixed with another crude oil or is applied with thermal hysteresis, such that resins in the vicinity of the asphaltene are separated. Therefore, a shape of the asphaltene is changed into a solid shape.

In addition, the crude oil sludge may further include water regardless of a kind of crude oil. The water is included in the crude oil sludge to form a kind of film in the vicinity of the asphaltene. The asphaltene is three-dimensionally bridged and other reins are solvated, such that the film may be a cause of allowing the asphaltene to form the emulsion without being phase-separated from a crude oil component. Therefore, the asphaltene having an emulsion shape is a component that is the most difficult to be separated in processing the-crude oil sludge, and it is difficult to separate the asphaltene having the emulsion shape by centrifugation, or the like.

Although the step a) according to the present invention may be changed depending on compositions of the crude oil and the sludge, it may be performed by any one or two or more selected among a mechanical separating method such as a filtering method using a filter, or the like, an agitating method, a manual method (method of discharging the sludge to the outside of the tank using a person or a machine), or the like, a. thermal separating method of dissolving and pulverizing the sludge using heated crude oil or hot water, a solvent extracting method of injecting a solvent or a chemical dissolving the sludge into the tank to provide fluidity to the sludge, a sound wave separating method, and a chemical separating method.

Next, the recovered sludge is subjected to a step of separating the sludge into the recovery oil, the water, and the sediment like the step b), such that only the recovery oil may be recovered.

According to the present invention, in the step b), a separating method is not limited, but may be selected among various methods depending on a composition of the sludge and a method of removing the sludge. As an example, as disclosed in Korean Patent No. 10-0475172, the sludge stations at a temperature of 60° C. or more, preferably, 60 to 130° C., thereby making it possible to phase-separate the sediment and the water from the recovery oil. Here, the reason why the sludge is heated is that viscosity of the sludge is decreased, such that a removal rate of the sediment is improved. In addition, an additive such as a dispersing agent, or the like, may be additionally injected, if necessary. Meanwhile, this process may be performed in the crude oil tank or be performed in a separate storage space connected to the crude oil tank. Alternatively, as disclosed in Japanese Patent Laid-Open Publication No. 2012-229403, a method of heating the sludge to evaporate the recovery oil included in the sludge and then recovering the recovery oil through cooling may also be performed.

The recovery oil separated according to the exemplary embodiment of the present invention may be recycled through a step of mixing the recovery oil with the crude oil and performing the fractional distillation on the mixture of the recovery oil and the crude like the step c). In more detail, in the step c) according to the present invention, the crude oil and the recovery oil may be mixed with each other by any one or two or more selected among c1) a method of mixing the recovery oil with the crude oil using a line mixer and transferring the mixture to a charge pump; c2) a method of periodically mixing the recovery oil with the crude oil and transferring the mixture to the charge pump; and c3) a method of mixing the recovery oil with the crude oil passing through the charge pump and transferring the mixture to a desalter, and the fractional distillation may be performed on the mixture of the recovery oil and the crude oil.

Among them, c1) may further include c1-1) a step of mixing the recovery oil with the crude oil using the line mixer; and c1-2) a step of transferring the crude oil mixed with the recovery oil to the charge pump.

This will be described in more detail with reference to FIG. 1. The recovery oil separated from the water and the sediment through the phase separation may be mixed with the crude oil passing through the charge pump as illustrated in

and then pass through the line mixer. The crude oil passing through the line mixer to thereby be sufficiently mixed with the recovery oil may be again supplied to the charge pump as illustrated in

and be then transferred to a crude distillation unit (CDU) process. However, in order to more smoothly mix the recovery oil and the crude oil with each other, the crude oil passing through a process of

may be again sent to a process of

and be circulated. In addition, in a circulation process, the recovery oil is continuously injected, such that a process of mixing the recovery oil and the crude oil with each other through the line mixer simultaneously with circulating the crude oil may be continuously performed.

In addition, crude oil stored in the crude oil tank rather than a crude oil charge tank may be mixed by the same method. First, the recovery oil manufactured through the phase separation may be mixed with the crude oil in the crude oil tank, as illustrated in

, and then pass through the line mixer. The crude oil passing through the line mixer to thereby be sufficiently mixed with the recovery oil may be again transferred to the crude oil tank, as illustrated in

, pass through the crude oil charge tank and the charge pump, and be then transferred to the crude distillation unit process. In addition, the crude oil with which the recovery oil of

is mixed may be sent to a process of

in which it is again mixed with the recovery oil and be circulated. In this circulation process, the recovery oil is continuously injected, such that a process of mixing the recovery oil and the crude oil with each other through the line mixer simultaneously with circulating the crude oil may be continuously performed.

In the method c1) according to the exemplary embodiment of the present invention, the number of circulations is not limited, and a kind, a size, a form, and the number of line mixers are not limited. As an example, several members may be disposed in the line mixer to adjust a flow velocity in the line mixer, and static mixers and Sulzer mixers may be alternately mounted in the line mixer.

In the method c1) according to the exemplary embodiment of the present invention, processes of

to

may be simultaneously performed. That is, the recovery oil phase-separated from the sludge and the crude oil coming from the crude oil tank may be mixed with as illustrated in {circle around (3)}, pass through the line mixer, and be sent to

. The crude oil passing through the line mixer is not directly sent from the crude oil tank to the crude oil charge tank, but may be circulated as in the process of

. In addition, the crude oil subjected to the processes of

and

may be transferred from the crude oil tank to the crude oil charge tank and the charge pump, be sent to a front end of the line mixer through the process of

to thereby be again mixed with the recovery oil, and pass through the line mixer and be then sent to a front end of the charge pump as illustrated in

. Even in this case, the crude oil passing through the charge pump is not directly sent to the crude distillation unit process, but may be sent to the process of

and be again circulated.

The method c2) according to the exemplary embodiment of the present invention is a method of adjusting a period in which the crude oil and the recovery oil are mixed with each other at the time of being mixed with each other. Since the recovery oil generally has a very high pour point, it is changed into a gel-phase at the time of being mixed with the crude oil at room temperature. The gel-phase recovery oil may not pass through a strainer used to filter impurities in front of the charge pump.

In the case in which the recovery oil is continuously mixed with the crude oil, there is a risk that the strainer will be clogged by the gel-phase recovery oil. In the method c2) according to the exemplary embodiment of the present invention, a period in which the recovery oil is supplied is adjusted at the time of mixing the crude oil and the recovery oil with each other, thereby making it possible to solve a phenomenon that the strainer in front of the charge pump is clogged. That is, although the gel-phase recovery oil may remain in the strainer without passing through the strainer, only the crude oil passes through the strainer during a period in which injection of the recovery oil is stopped, such that the recovery oil strained by the strainer may be cleaned and pass through the strainer by a flow of the crude oil.

A step c2) will be described below with reference to FIG. 2. The recovery oil phase-separated and generated from the sludge is mixed with the crude oil stored in the crude oil charge tank. Here, a position at which the recovery oil is injected is in front of the charge pump, and the recovery oil may be directly mixed with the crude oil without introducing the line mixer. A mixing period of the recovery oil may be freely changed depending on compositions of the sludge and the recovery oil, fluidity of the recovery oil, and the like, and a period in which the supply of the recovery oil is stopped for 0.2 to 1 hour may be present after the recovery oil is injected for 0.5 to 3 hours. That is, in order to clean the recovery oil remaining in the strainer without passing through the strainer due to the injection of the recovery oil, the period in which the supply of the recovery oil is stopped for 0.2 to 1 hour is present.

The method c3) according to the exemplary embodiment of the present invention is a method of securing fluidity of the recovery oil by preheating the crude oil at the time of mixing the crude oil and the recovery oil with each other.

Generally, when the crude oil is fractionally distilled, it is heated to 340 to 360° C. to thereby be divided into liquefied petroleum gas (LPG), gasoline, naphtha, kerosene, diesel, heavy oil, and the like, based on a boiling point. Here, in order to recover thermal energy applied to a distillation column, a heat exchanger (preheater, preheat exchanger, or the like) is disposed to heat the crude oil before being desalted. When the crude oil is preheated through the heat exchanger, the crude oil having a room temperature or a temperature slightly higher than the room temperature is preheated to a temperature of 100° C. or more. Since this preheating temperature exceeds a pour point (70° C.) of the recovery oil, as soon as the recovery oil is mixed with the crude oil, it has high fluidity, such that the recovery oil and the crude oil may be uniformly mixed with each other.

FIG. 3 illustrates the method c3) according to the exemplary embodiment of the present invention. The recovery oil phase-separated and generated from the sludge may be injected into and mixed with the crude oil passing through the preheater. Here, the crude oil passing through the preheater may be preheated to a temperature of the pour point or more of the recovery oil, preferably, temperature of 90 to 150° C. In addition, the recovery oil may be periodically injected as in c2) or be continuously injected, and the crude oil may pass through the desalter and be then preheated through the preheater in order for the recovery oil and the crude oil to be more uniformly mixed with each other.

In the present invention, 0.1 to 2 parts by weight of recovery oil may be mixed with 100 parts by weight of crude oil. In the case in which parts by weight of mixed recovery oil exceeds 2 parts by weight, the recovery oil is not smoothly mixed with the crude oil, such that it is difficult to secure fluidity of the recovery oil, and impurities in the recovery oil occlude facilities such as a heating furnace, a pipe, and the like, or are accumulated on inner walls of the facilities, such that process efficiency may be significantly decreased.

In addition, in the recycling method of recovery oil according to the exemplary embodiment of the present invention, additives such as a neutralizing agent, an emulsification preventing agent, a metal pollution removing agent, a stabilizer, and the like, may be further included, in some cases. Particularly, when an excessively large amount of caustic material is present, a process of stabilizing and separating an asphaltene-water mixture may be hindered due to a fatty acid, and in the case in which the crude oil and the water are excessively strongly mixed with each other, emulsion that is difficult to be decomposed may be formed. Therefore, it is preferable that the neutralizing agent and the emulsification preventing agent that may adjust stability of the asphaltene-water mixture are added. These additives may be injected in the middle of a process, and may be injected in any step without departing the scope of the present invention.

In addition, in the recycling method of recovery oil according to the exemplary embodiment of the present invention, a condensate may be further mixed at the time of mixing the crude oil and the recovery oil with each other.

The condensate according to the present invention means a liquid-phase hydrocarbon mixture obtained through a condensing process of condensing high boiling point materials by a physical phase change by compressing and cooling a gas mixture and having carbons of 1 to 7. Since the condensate is a hydrocarbon having a small number of carbons, it may have low viscosity to improve mixing efficiency between the recovery oil and the crude oil.

The recycling method of recovery oil according to present invention will be described in more detail through Inventive Examples and. Comparative Examples. However, the following Inventive Examples and Comparative Examples are only examples for describing the present invention in more detail, and the present invention is not limited by Inventive Examples and Comparative Examples.

Components of materials and physical property measuring methods used in Inventive Examples and Comparative Examples are as follows.

(Crude Oil)

Properties and mixing ratios of crude oils through Inventive Examples are illustrated in the following Tables 1 and 2.

TABLE 1 Division Crude Oil 1 Crude Oil 2 Property Specific Gravity 0.8234 0.8189 (15/4° C.) Sulfur, wt. % 1.5 1.5 Nitrogen, ppm 1447 1365 Water and Sediment, 0.05 0.05 vol. % Carbon Residue, 3.91 3.92 wt. % Salinity, ptb 5.7 5.8 Iron, ppm 7 2 Vanadium, ppm 25 26 Nickel, ppm 8 7 Yield    C5~75° C. 4.4 4.7 (wt. %)  75~155° C. 12.5 13.6 155~235° C. 17.2 17.5 235~350° C. 17.1 16 350~360° C. 1.3 1.2     360° C.~ 47.7 46.9

TABLE 2 Mixing Ratio (vol. %) Division KWT ARH RAS MPC SNP TNG KFC ROD MEL SRN Sum Crude Oil 1 29.2 19.1 9.4 12.5 4.1 3.4 12.7 3.6 1.4 4.5 100.0 Crude Oil 2 26.5 19.8 8.8 12.1 3.3 3.3 14.9 2.8 3.6 4.8 100.0

(Sludge and Recovery Oil After Being Phase-Separated)

Properties of the sludge and the recovery oil after a phase-separation process are illustrated in the following Table 3.

TABLE 3 Division Sludge Recovery Oil Property Specific Gravity Measurement 0.8700 (15/4° C.) is impossible Pour Point, ° C. Measurement 70 is impossible Carbon Residue, — 5.85 wt. % Salinity, ptb — 56 Iron, mg/kg 2,983 1,997 Vanadium, mg/kg 27 27 Nickel, mg/kg 8 10 Yield,    C5~75° C. 1.2 1.6 wt. %  75~155° C. 7.4 9.2 155~235° C. 8.9 12.7 235~350° C. 9.2 15.3 350~360° C. 0.7 1.1     360° C.~ 72.6 60.2

(Property of Mixed Oil)

Physical properties of mixed oil used in Inventive Examples were measured by the following method.

Sulfur: A total of sulfur was measured using a monochromatic wavelength-dispersive X-ray fluorescence (MWDXRF) spectrometry depending on ASTM D7039 (Standard Test Method for Sulfur in Gasoline and Diesel Fuel by Monochromatic Wavelength Dispersive X-ray Fluorescence Spectrometry).

Nitrogen: A content was calculated by burning a sample at a temperature of 1,000° C. using an element analyzer (EA-CHNS) to decompose the sample into gas and measuring thermal conductivity of the gas.

Micro-Carbon Residue (MCR): An amount of carbon residue remaining after evaporation and thermal decomposition of a substrate was measured depending on ASTM D450.

Metal Content: Each of contents of iron, vanadium, and nickel was measured using an inductively coupled plasma-atomic emission spectrometer (ICP-AES).

Salinity: Salinity was measured using a salt analyzer depending on ASTM D3230.

(Yield)

A sample was measured using a gas chromatography frame ionization detector (GC-FID).

INVENTIVE EXAMPLE 1

1,400 tons of sludge collected in a crude oil charge tank was transferred to a centrifugation tank of 80° C. and was phase-separated. Water and sediment were separately separated from the sludge through the phase separation, and 1,000 tons of remaining recovery oil was recovered.

Separately from the above-mentioned process, Crude Oil 1 in Table 1 stored in the crude oil charge tank passed through a charge pump and was then mixed with the recovery oil. Here, a mixing amount was illustrated in the following Table 4, and the crude oil and the recovery oil passed through a line mixer immediately after they were mixed with each other, such that they were uniformly mixed with each other. The crude oil of which mixing is ended was again supplied to the charge pump and was sent to a CDU process to thereby be crude-distilled. Here, a crude oil sample was collected, and properties of mixed oil of the crude oil and the recovery oil and yields depending on a fractional distillation temperature were measured and illustrated in the following Table 4.

INVENTIVE EXAMPLE 2

1,400 tons of sludge collected in a crude oil charge tank was transferred to a centrifugation tank of 80° C. and was phase-separated. Water and sediment were separately separated from the sludge through the phase separation, and 1,000 tons of remaining recovery oil was recovered.

Separately from the above-mentioned process, Crude Oil 2 in Table 1 stored in the crude oil charge tank passed through a charge pump and was then mixed with the recovery oil. Here, a mixing amount was illustrated in the following Table 4, and the crude oil and the recovery oil passed through a line mixer immediately after they were mixed with each other, such that they were uniformly mixed with each other. The crude oil of which mixing is ended was again supplied to the charge pump and was sent to a CDU process to thereby be crude-distilled. Here, a crude oil sample was collected, and properties of mixed oil of the crude oil and the recovery oil and yields depending on a fractional distillation temperature were measured and illustrated in the following Table 4.

COMPARATIVE EXAMPLE 1

Fractional distillation was performed using the same method as that of Inventive Example 1 except that the recovery oil is not mixed. Here, a crude oil sample was collected, and properties and yields depending on a fractional distillation temperature were measured and illustrated in the following Table 4.

COMPARATIVE EXAMPLE 2

Fractional distillation was performed using the same method as that of Inventive Example 2 except that the recovery oil is not mixed. Here, a crude oil sample was collected, and properties and yields depending on a fractional distillation temperature were measured and illustrated in the following Table 4.

TABLE 4 Inventive Inventive Inventive Inventive Inventive Inventive Comparative Comparative Division Example 1-1 Example 1-2 Example 1-3 Example 2-1 Example 2-2 Example 2-3 Example 1 Example 2 Mixing Crude Oil 100 100 100 100 100 100 100 100 Condition (mL) Recovery 0.5 1 2 0.5 1 2 0 0 Oil (g) Property Sulfur, 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 wt. % Nitrogen, 1384 1459 1400 1354 1277 1282 1447 1365 ppm Water and 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Sediment, vol. % Carbon 3.87 4.31 3.79 3.76 3.74 3.84 3.91 3.92 Residue, wt. % Salinity, 5.8 6.5 6.7 5.8 6.4 6.8 5.7 5.8 ptb Iron, ppm 18 23 32 11 19 32 7 2 Vanadium, 25 26 27 25 26 25 25 26 ppm Nickel, 7 7 8 8 8 8 8 7 ppm Yield  C5~75° C. 4.4 3.9 5.5 5.2 5.8 5.8 4.4 4.7 (wt. %)  75~155° C. 11.7 11.8 12.1 12.1 12.6 12.6 12.5 13.6 155~235° C. 17.8 17.8 17 17.7 17.4 16.6 17.2 17.5 235~350° C. 17.2 17.2 16.1 15.8 15.1 14.6 17.1 16 350~360° C. 1.3 1.3 1.1 1.2 1.1 1.1 1.3 1.2 360° C.~ 47.6 48 48.3 48.0 48.0 49.3 47.7 46.9

As illustrated in Table 4, it may be appreciated that crude oil subjected to the recycling method according to the present invention maintains similar compositions without increasing components other than iron and salinity in a property. Although an oil separation time tends to be increased due to an increase in a content of salinity, a decrease in oil separation efficiency may be prevented by injecting the emulsification preventing agent. In addition, it may be appreciated that similar numerical values are shown regardless of a temperature in terms of a yield, such that even though the recovery oil is mixed, it may be effectively recycled without having a large influence on the properties and the yields.

In the recycling method of recovery oil according to the present invention in which the recovery oil separated from the sludge accumulated in the crude oil tank is recycled, a limitation in a storage feature of the crude tank depending on the accumulation of the sludge may be solved. In addition, disadvantages of the recovery oil such as a high pour point, a low flash point, and a high content of impurities are overcome, and fractional distillation is performed, thereby making it possible to expect a profitability improving effect. Further, a process cost decrease effect depending on processing of the sludge may be accomplished, and a waste processing cost may be significantly decreased.

Although the exemplary embodiments of the present invention have been described hereinabove, various modifications and alterations and equivalents of the present invention are possible, and the exemplary embodiments may be appropriately modified and similarly applied. Therefore, contents described in the exemplary embodiments do not limit the scope of the present invention as defined by the claims. 

What is claimed is:
 1. A recycling method of recovery oil comprising the steps of: a) recovering sludge accumulated in a crude oil tank; b) separating the sludge into recovery oil, water, and sediment; and c) mixing the recovery oil with crude oil and performing fractional distillation on a mixture of the recovery oil and the crude oil.
 2. The recycling method of recovery oil of claim 1, wherein in step c), the recovery oil and the crude oil are mixed with each other by any one or two or more selected among c1) a method of mixing the recovery oil with the crude oil using a line mixer and transferring the mixture to a charge pump; c2) a method of periodically mixing the recovery oil with the crude oil and transferring the mixture to the charge pump; and c3) a method of mixing the recovery oil with the crude oil passing through the charge pump and transferring the mixture to a desalter.
 3. The recycling method of recovery oil of claim 2, wherein c1) includes: c1-1) mixing the recovery oil with the crude oil using the line mixer; and c1-2) transferring the crude oil mixed with the recovery oil to the charge pump.
 4. The recycling method of recovery oil of claim 3, wherein the crude oil passing through step c1-2) is again sent to step c1-1) and is circulated.
 5. The recycling method of recovery oil of claim 2, wherein in step c2), a process of stopping the supply of the recovery oil for 0.2 to 1 hour after the recovery oil is supplied and mixed with the crude oil for 0.5 to 3 hours is repeated.
 6. The recycling method of recovery oil of claim 2, wherein the crude oil of c3) is preheated to a temperature of a pour point or more of the recovery oil.
 7. The recycling method of recovery oil of claim 6, wherein the crude oil is preheated to a temperature of 90 to 150° C.
 8. The recycling method of recovery oil of claim 2, wherein 0.1 to 2 parts by weight of the recovery oil are mixed with 100 parts by weight of the crude oil.
 9. The recycling method of recovery oil of claim 1, wherein step a) is performed by any one or two or more selected among a mechanical separating method, a thermal separating method, a solvent extracting method, a sound wave separating method, and a chemical separating method. 